Field strength meter -- diode...

[Jeff Layman]

On 01/01/2022 01:19, whit3rd wrote:

On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote:
On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote:

https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html

the circuit needs a closed DC path in order for current to flow.



Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
to the microvolt output of something like this? -- thanks

https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html

A moving-needle meter for 30 uA with 100 ohms internal resistance can cover the
3mV range, with 30 uV easily resolved. Add a battery for collector bias, and
use a low-noise transistor B-E instead of one diode, and you\'re good for lower signals.

So low, in fact, that some frequency tuning is a wise addition.

Excuse my ignorance, but why in the \"Description\" does it say that it\'s
a \"-30-0-30µA Galvanometer\", but in the \"Specification\" say \"Sensitive
Range: -300-0-300μA\"?

And what is the 2.4kohm resistor for? \"Instruction\" 2 states \"When it is
connected in series in the circuit, the higher end of the \"G\" terminal
is used.\" That would give it an FSD of 72mV, wouldn\'t it? Is there a
reason why it\'s 2.4kohm rather than another value?

--

Jeff

 

[whit3rd]

On Friday, December 31, 2021 at 11:56:07 PM UTC-8, Jeff Layman wrote:

On 01/01/2022 01:19, whit3rd wrote:
On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote:
On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote:

https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html

the circuit needs a closed DC path in order for current to flow.



Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
to the microvolt output of something like this? -- thanks

https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html

Excuse my ignorance, but why in the \"Description\" does it say that it\'s
a \"-30-0-30µA Galvanometer\", but in the \"Specification\" say \"Sensitive
Range: -300-0-300μA\"?

Yeah, that\'s a mystery.

And what is the 2.4kohm resistor for? \"Instruction\" 2 states \"When it is
connected in series in the circuit, the higher end of the \"G\" terminal
is used.\" That would give it an FSD of 72mV, wouldn\'t it? Is there a
reason why it\'s 2.4kohm rather than another value?

It\'s usual in these things to provide some damping (a shunt resistor or R-C
snubber) across the bare galvanometer, and there\'s a particular value
that (with the coil inductance) is most effective. That\'s the only
resistor value I\'d expect to see built-in. The merchant might not
know what it\'s for, but damping makes the needle return to zero
between measurements instead of oscillating for a few seconds.

 

[Jeff Layman]

On 01/01/2022 08:28, whit3rd wrote:

On Friday, December 31, 2021 at 11:56:07 PM UTC-8, Jeff Layman wrote:
On 01/01/2022 01:19, whit3rd wrote:
On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote:
On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote:

https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html

the circuit needs a closed DC path in order for current to flow.



Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react
to the microvolt output of something like this? -- thanks

https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html

Excuse my ignorance, but why in the \"Description\" does it say that it\'s
a \"-30-0-30µA Galvanometer\", but in the \"Specification\" say \"Sensitive
Range: -300-0-300μA\"?

Yeah, that\'s a mystery.

Probably just a misprint or mistranslation.

And what is the 2.4kohm resistor for? \"Instruction\" 2 states \"When it is
connected in series in the circuit, the higher end of the \"G\" terminal
is used.\" That would give it an FSD of 72mV, wouldn\'t it? Is there a
reason why it\'s 2.4kohm rather than another value?

It\'s usual in these things to provide some damping (a shunt resistor or R-C
snubber) across the bare galvanometer, and there\'s a particular value
that (with the coil inductance) is most effective. That\'s the only
resistor value I\'d expect to see built-in. The merchant might not
know what it\'s for, but damping makes the needle return to zero
between measurements instead of oscillating for a few seconds.

OK. Makes sense. Just don\'t try try to push it to -300-0-300μA!

--

Jeff

 

[Phil Hobbs]

Jan Frank wrote:

whit3rd <whit3rd@gmail.com> wrote:

https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Senso
r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.ht
ml

The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in
parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn\'t drift.

With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps.

My favorite electrometer is the Kiethley 610C, which only goes down to 1e-
11 A full scale, and drifts like hell.

Nah, there\'s the range multiplier knob that gets you another factor of
100 on the FS range, so you get a 10-fA FSR on that box.

Of course that one is too unstable to be useful, but the 100-fA FS range
is pretty good, at least on my unit. Yours may need cleaning or repair.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Jan Frank]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

Jan Frank wrote:
whit3rd <whit3rd@gmail.com> wrote:

https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sen
so
r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.
ht ml

The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in
parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn\'t drift.

With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps.

My favorite electrometer is the Kiethley 610C, which only goes down to
1e-11 A full scale, and drifts like hell.

Nah, there\'s the range multiplier knob that gets you another factor of
100 on the FS range, so you get a 10-fA FSR on that box.

Of course that one is too unstable to be useful, but the 100-fA FS range
is pretty good, at least on my unit. Yours may need cleaning or repair.

Cheers

Phil Hobbs

There is no change when the range switch is partially rotated, so I don\'t
think it is the problem. The reading simply wanders, and it gets worse as
you go downrange. Obviously thermal drift.

I was thinking of replacing the input transistors with an LMC660 or modern
equivalent and may do so if I ever need to monitor weak currents over a
period of time.

But a better option would be to get a used 616 which offers autoranging
and noise of 2e-15 p-p on the lowest current range. It is pretty cheap on
eBay - around $295 or so. But for now, the RM109 is more than adequate. It
certainly beats the banggood galvanometer.

 

[mkr5000]

On Sunday, January 2, 2022 at 12:50:01 AM UTC-5, Jan Frank wrote:

Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:

Jan Frank wrote:
whit3rd <whi...@gmail.com> wrote:

https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sen
so
r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.
ht ml

The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in
parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn\'t drift.

With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps.

My favorite electrometer is the Kiethley 610C, which only goes down to
1e-11 A full scale, and drifts like hell.

Nah, there\'s the range multiplier knob that gets you another factor of
100 on the FS range, so you get a 10-fA FSR on that box.

Of course that one is too unstable to be useful, but the 100-fA FS range
is pretty good, at least on my unit. Yours may need cleaning or repair.

Cheers

Phil Hobbs
There is no change when the range switch is partially rotated, so I don\'t
think it is the problem. The reading simply wanders, and it gets worse as
you go downrange. Obviously thermal drift.

I was thinking of replacing the input transistors with an LMC660 or modern
equivalent and may do so if I ever need to monitor weak currents over a
period of time.

But a better option would be to get a used 616 which offers autoranging
and noise of 2e-15 p-p on the lowest current range. It is pretty cheap on
eBay - around $295 or so. But for now, the RM109 is more than adequate. It
certainly beats the banggood galvanometer.

I ordered some parts and have yet to breadboard anything yet for a FSM. Got the schottkys and a couple germanium diode varieties, plus an FET.

What exactly is the value in this where he 2 diodes in series? Of course it\'s on youtube so....

https://www.youtube.com/watch?v=kml8pNNGTvU&ab_channel=GEORGECHANIOTAKIS

 

[Phil Hobbs]

Jan Frank wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

Jan Frank wrote:
whit3rd <whit3rd@gmail.com> wrote:

https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sen
so
r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.
ht ml

The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in
parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn\'t drift.

With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps.

My favorite electrometer is the Kiethley 610C, which only goes down to
1e-11 A full scale, and drifts like hell.

Nah, there\'s the range multiplier knob that gets you another factor of
100 on the FS range, so you get a 10-fA FSR on that box.

Of course that one is too unstable to be useful, but the 100-fA FS range
is pretty good, at least on my unit. Yours may need cleaning or repair.

Cheers

Phil Hobbs

There is no change when the range switch is partially rotated, so I don\'t
think it is the problem. The reading simply wanders, and it gets worse as
you go downrange. Obviously thermal drift.

Both JL and I have 610Cs that are far better than that. Yours must
broken or badly contaminated. Mine easily measures down to the tens of
femtoamps.

I was thinking of replacing the input transistors with an LMC660 or modern
equivalent and may do so if I ever need to monitor weak currents over a
period of time.

You can do a good job with that. I\'ve been meaning to build a nice
100-pF charge-dispensing loop electrometer, but so far the 610C or even
the old tube-based 405 have been better than good enough.

But a better option would be to get a used 616 which offers autoranging
and noise of 2e-15 p-p on the lowest current range. It is pretty cheap on;
eBay - around $295 or so.

I haven\'t got a lot of use for a digital electrometer. Down in the
picoamps and lower, seeing trends is much more important than high
precision, not least because leakages are very unlikely to be stable to
3 sig figures.

(Plus I paid $5 plus shipping for my 405, $36 for a 602C, and $125 for
the 610C on my bench.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[server]

On Sun, 2 Jan 2022 09:47:33 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

Jan Frank wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

Jan Frank wrote:
whit3rd <whit3rd@gmail.com> wrote:

https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sen
so
r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.
ht ml

The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in
parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn\'t drift.

With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps.

My favorite electrometer is the Kiethley 610C, which only goes down to
1e-11 A full scale, and drifts like hell.

Nah, there\'s the range multiplier knob that gets you another factor of
100 on the FS range, so you get a 10-fA FSR on that box.

Of course that one is too unstable to be useful, but the 100-fA FS range
is pretty good, at least on my unit. Yours may need cleaning or repair.

Cheers

Phil Hobbs

There is no change when the range switch is partially rotated, so I don\'t
think it is the problem. The reading simply wanders, and it gets worse as
you go downrange. Obviously thermal drift.

Both JL and I have 610Cs that are far better than that. Yours must
broken or badly contaminated. Mine easily measures down to the tens of
femtoamps.

The fast feedback mode on mine has never worked, so fA and tohm
measurements are super slow, 10s of minutes sometimes. Things have to
be shielded or people walking around will pin the needle.

I built my own fA parts tester before I got the Keithley, using an
LMC6001 cmos opamp. It has less wiring and no switches so tends to be
faster.

https://www.dropbox.com/sh/aj85edzmmrx7ret/AAA6HYPHyVeBrCeKShvq82ega?dl=0

I was thinking of replacing the input transistors with an LMC660 or modern
equivalent and may do so if I ever need to monitor weak currents over a
period of time.

You can do a good job with that. I\'ve been meaning to build a nice
100-pF charge-dispensing loop electrometer, but so far the 610C or even
the old tube-based 405 have been better than good enough.


But a better option would be to get a used 616 which offers autoranging
and noise of 2e-15 p-p on the lowest current range. It is pretty cheap on;
eBay - around $295 or so.

I haven\'t got a lot of use for a digital electrometer. Down in the
picoamps and lower, seeing trends is much more important than high
precision, not least because leakages are very unlikely to be stable to
3 sig figures.

(Plus I paid $5 plus shipping for my 405, $36 for a 602C, and $125 for
the 610C on my bench.

Cheers

Phil Hobbs

--

I yam what I yam - Popeye

 

[mkr5000]

On Sunday, January 2, 2022 at 11:05:45 AM UTC-5, jla...@highlandsniptechnology.com wrote:

On Sun, 2 Jan 2022 09:47:33 -0500, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

Jan Frank wrote:
Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote:

Jan Frank wrote:
whit3rd <whi...@gmail.com> wrote:

https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sen
so
r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.
ht ml

The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in
parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn\'t drift.

With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps.

My favorite electrometer is the Kiethley 610C, which only goes down to
1e-11 A full scale, and drifts like hell.

Nah, there\'s the range multiplier knob that gets you another factor of
100 on the FS range, so you get a 10-fA FSR on that box.

Of course that one is too unstable to be useful, but the 100-fA FS range
is pretty good, at least on my unit. Yours may need cleaning or repair.

Cheers

Phil Hobbs

There is no change when the range switch is partially rotated, so I don\'t
think it is the problem. The reading simply wanders, and it gets worse as
you go downrange. Obviously thermal drift.

Both JL and I have 610Cs that are far better than that. Yours must
broken or badly contaminated. Mine easily measures down to the tens of
femtoamps.
The fast feedback mode on mine has never worked, so fA and tohm
measurements are super slow, 10s of minutes sometimes. Things have to
be shielded or people walking around will pin the needle.

I built my own fA parts tester before I got the Keithley, using an
LMC6001 cmos opamp. It has less wiring and no switches so tends to be
faster.

https://www.dropbox.com/sh/aj85edzmmrx7ret/AAA6HYPHyVeBrCeKShvq82ega?dl=0

I was thinking of replacing the input transistors with an LMC660 or modern
equivalent and may do so if I ever need to monitor weak currents over a
period of time.

You can do a good job with that. I\'ve been meaning to build a nice
100-pF charge-dispensing loop electrometer, but so far the 610C or even
the old tube-based 405 have been better than good enough.


But a better option would be to get a used 616 which offers autoranging
and noise of 2e-15 p-p on the lowest current range. It is pretty cheap on;
eBay - around $295 or so.

I haven\'t got a lot of use for a digital electrometer. Down in the
picoamps and lower, seeing trends is much more important than high
precision, not least because leakages are very unlikely to be stable to
3 sig figures.

(Plus I paid $5 plus shipping for my 405, $36 for a 602C, and $125 for
the 610C on my bench.

Cheers

Phil Hobbs


--
I yam what I yam - Popeye

Maybe you guys didn\'t see this but why the (2) diodes in series (4 total) as shown here?
Thanks.

https://www.youtube.com/watch?v=kml8pNNGTvU&ab_channel=GEORGECHANIOTAKIS

 

[whit3rd]

On Sunday, January 2, 2022 at 9:30:04 AM UTC-8, mkr5000 wrote:

Maybe you guys didn\'t see this but why the (2) diodes in series (4 total) as shown here?
Thanks.

https://www.youtube.com/watch?v=kml8pNNGTvU&ab_channel=GEORGECHANIOTAKIS

Probably to keep the sensitivity low. Read some of the comments; a fluorescent lamp
(probably electronic ballast, few kilohertz current fluctuations) reads as REAL hot.

What you usually want, is something to read a particular range of frequencies, usually in
a known RF band, which means at least a grid-dip meter kind of gizmo. I\'m partial to
the use of AGC-type amplifiers, where one infers high RF strength from low amplifier
bias.

So, what I\'d find really useful, is a way to put an ADL5906 into
my old grid dip meter...

<https://www.analog.com/en/products/adl5906.html>

but I suspect it\'s harder to do that, than it was to make a solid-state plugin to
replace the tube for output-only GDO functions.

 

[Tom Del Rosso]

jlarkin@highlandsniptechnology.com wrote:

I built my own fA parts tester before I got the Keithley, using an
LMC6001 cmos opamp. It has less wiring and no switches so tends to be
faster.

https://www.dropbox.com/sh/aj85edzmmrx7ret/AAA6HYPHyVeBrCeKShvq82ega?dl=0

The components are separated by some kind of stand-off that mustn\'t leak
a femptoamp. What material is that?


--
Defund the Thought Police
Andiamo Brandon!

 

[server]

On Sun, 2 Jan 2022 17:23:07 -0500, \"Tom Del Rosso\"
<fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:

I built my own fA parts tester before I got the Keithley, using an
LMC6001 cmos opamp. It has less wiring and no switches so tends to be
faster.

https://www.dropbox.com/sh/aj85edzmmrx7ret/AAA6HYPHyVeBrCeKShvq82ega?dl=0

The components are separated by some kind of stand-off that mustn\'t leak
a femptoamp. What material is that?

The Rat Shack binding posts were super leaky so I hacked a hole in the
box and added a lexan sheet.

The terminal strip inside is a ceramic strip as used in old Tek
scopes, but the critical node is a mid-air junction.



--

I yam what I yam - Popeye

 

[Phil Hobbs]

Tom Del Rosso wrote:

jlarkin@highlandsniptechnology.com wrote:

I built my own fA parts tester before I got the Keithley, using an
LMC6001 cmos opamp. It has less wiring and no switches so tends to be
faster.

https://www.dropbox.com/sh/aj85edzmmrx7ret/AAA6HYPHyVeBrCeKShvq82ega?dl=0

The components are separated by some kind of stand-off that mustn\'t leak
a femptoamp. What material is that?


Looks like a surplus Tektronix ceramic terminal strip.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[server]

On Sun, 2 Jan 2022 18:01:21 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

Tom Del Rosso wrote:
jlarkin@highlandsniptechnology.com wrote:

I built my own fA parts tester before I got the Keithley, using an
LMC6001 cmos opamp. It has less wiring and no switches so tends to be
faster.

https://www.dropbox.com/sh/aj85edzmmrx7ret/AAA6HYPHyVeBrCeKShvq82ega?dl=0

The components are separated by some kind of stand-off that mustn\'t leak
a femptoamp. What material is that?


Looks like a surplus Tektronix ceramic terminal strip.

Cheers

Phil Hobbs

Yes. I got a box of unused ones at the Foothill Flea Market.



--

I yam what I yam - Popeye

 

[Rich S]

On Sunday, January 2, 2022 at 11:01:29 PM UTC, Phil Hobbs wrote:

Tom Del Rosso wrote:
jla...@highlandsniptechnology.com wrote:

I built my own fA parts tester before I got the Keithley, using an
LMC6001 cmos opamp. It has less wiring and no switches so tends to be
faster.

https://www.dropbox.com/sh/aj85edzmmrx7ret/AAA6HYPHyVeBrCeKShvq82ega?dl=0

The components are separated by some kind of stand-off that mustn\'t leak
a femptoamp. What material is that?


Looks like a surplus Tektronix ceramic terminal strip.
Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Ah, yes. Thanks Phil, for naming those.
We have a drawer full of those
back in the lab. Their purpose is obvious
but I didn\'t know their origin.
(We have a lot of old Tek repair parts
tucked away, unless they were victims
of another \"5s+2 event\".)

John, thanks for sharing. Your
\"integrator\" is pretty leaky (Rf=510 R)
Is that Cf a \'virtual capacitor\'? It seems
to be hidden in the wiring photo.

The output caps, Are they special film
that you chose to minimize Dielectric Absorption*?
Or given that the node impedances are so low
(220 R) any plastic is OK?
(*Ref: https://www.sciencedirect.com/topics/engineering/dielectric-absorption)

= RS

 

[Rich S]

I haven\'t got a lot of use for a digital electrometer. Down in the
picoamps and lower, seeing trends is much more important than high
precision, not least because leakages are very unlikely to be stable to
3 sig figures.

Phil, this is an excellent point, that I want to
amplify. Even if accuracy is lacking, the
precision and stability of a piece of equipment
(no matter how old it is) is still valuable.
Thanks! = RS

 

[server]

On Mon, 3 Jan 2022 06:59:17 -0800 (PST), Rich S
<richsulinengineer@gmail.com> wrote:

On Sunday, January 2, 2022 at 11:01:29 PM UTC, Phil Hobbs wrote:
Tom Del Rosso wrote:
jla...@highlandsniptechnology.com wrote:

I built my own fA parts tester before I got the Keithley, using an
LMC6001 cmos opamp. It has less wiring and no switches so tends to be
faster.

https://www.dropbox.com/sh/aj85edzmmrx7ret/AAA6HYPHyVeBrCeKShvq82ega?dl=0

The components are separated by some kind of stand-off that mustn\'t leak
a femptoamp. What material is that?


Looks like a surplus Tektronix ceramic terminal strip.
Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Ah, yes. Thanks Phil, for naming those.
We have a drawer full of those
back in the lab. Their purpose is obvious
but I didn\'t know their origin.
(We have a lot of old Tek repair parts
tucked away, unless they were victims
of another \"5s+2 event\".)

John, thanks for sharing. Your
\"integrator\" is pretty leaky (Rf=510 R)
Is that Cf a \'virtual capacitor\'? It seems
to be hidden in the wiring photo.

The opamp is a unity-gain follower. The 510r could be zero ohms, but I
thought I might add an offset pot some day, which I didn\'t.

The output caps, Are they special film
that you chose to minimize Dielectric Absorption*?

No, ordinary ceramics. We have a lot of RF in our place from Sutro
Tower, and I wanted to keep that out. Opamps like to rectify RF.

Or given that the node impedances are so low
(220 R) any plastic is OK?
(*Ref: https://www.sciencedirect.com/topics/engineering/dielectric-absorption)

= RS

The measurements are DC, slow, so DA is not a concern.

It worked terribly until I figured out that the RatShack nylon binding
posts were super leaky, and added the lexan plate. That was messy.

I have a set of Pomona banana plugs with various resistors from 1K to
1T ohms. One of those plugs in as Z1 or Z2, and the DUT becomes the
other. Then measure the two voltage drops.

Another aluminum chassis is used as a shield, upside down, and can be
bolted down. That avoids errors from local e-fields, like people
walking and breathing in the room, or 60 Hz fields.





--

I yam what I yam - Popeye

 

[Jan Panteltje]

On a sunny day (Sun, 09 Jan 2022 10:25:32 +0100) it happened Jeroen Belleman
<jeroen@nospam.please> wrote in <sre9mc$prb$1@gioia.aioe.org>:

On 2022-01-09 00:51, Clifford Heath wrote:
On 8/1/22 9:43 pm, Jeroen Belleman wrote:
On 2022-01-08 10:53, Jan Panteltje wrote:
PS see https://github.com/jdesbonnet/RCWL-0516

Now I just received some about 3 GHz? (still have to measure
it) doppler motion detectors that work through glass etc. from
a local shop, also for about 2 Euro a piece, on ebay those are
even cheaper: https://www.ebay.com/itm/311911747154 Is using
that frequency even legal here? Plenty of stuff play with!



Interesting gadget. I suppose Q1 does double duty as oscillator and
mixer. The schematics are of no help to figure out how it really
works. Anyone care to comment? The secret is all in the PCB layout
around Q1, clearly.

I believe it\'s the same approach that used to be used by the 10GHz
automatic door detectors that used to trigger automotive radar
detectors. Oscillator and mixer in one device, pick out the audio
Doppler signal.

CH

I gathered that much, yes. I was more interested in a discussion
of the PCB traces and how they work together to make an oscillator
and antenna.

I\'m trying to guess the signs of the reactances between the
terminals of Q1 at 3GHz. The trouble is that everything is
coupled to everything else and I\'m at a loss to tell what
is dominant. Every damn bit of trace around Q1 looks like
a resonator that could be either capacitive or inductive at
3GHz!

At least I\'m convinced that none of the actual /components/
on the schematic are involved in determining this oscillator.
(Except for Q1, of course.) It\'s all in the PCB traces.

Jeroen Belleman

Yes
it is all not so different from the twisted wire oscillator, but mine is simpler:
http://panteltje.com/pub/2.4GHz_twisted_oscillator_IMG_3629.GIF
circuit:
http://www.panteltje.com/pub/twisted_wire_oscillator_IMG_6629.JPG
probably can make my own GHz Doppler RF with that...

 

[Jeroen Belleman]

On 2022-01-09 11:56, Jan Panteltje wrote:

On a sunny day (Sun, 09 Jan 2022 10:25:32 +0100) it happened Jeroen Belleman
jeroen@nospam.please> wrote in <sre9mc$prb$1@gioia.aioe.org>:

On 2022-01-09 00:51, Clifford Heath wrote:
On 8/1/22 9:43 pm, Jeroen Belleman wrote:
On 2022-01-08 10:53, Jan Panteltje wrote:
PS see https://github.com/jdesbonnet/RCWL-0516

Now I just received some about 3 GHz? (still have to measure
it) doppler motion detectors that work through glass etc. from
a local shop, also for about 2 Euro a piece, on ebay those are
even cheaper: https://www.ebay.com/itm/311911747154 Is using
that frequency even legal here? Plenty of stuff play with!



Interesting gadget. I suppose Q1 does double duty as oscillator and
mixer. The schematics are of no help to figure out how it really
works. Anyone care to comment? The secret is all in the PCB layout
around Q1, clearly.

I believe it\'s the same approach that used to be used by the 10GHz
automatic door detectors that used to trigger automotive radar
detectors. Oscillator and mixer in one device, pick out the audio
Doppler signal.

CH

I gathered that much, yes. I was more interested in a discussion
of the PCB traces and how they work together to make an oscillator
and antenna.

I\'m trying to guess the signs of the reactances between the
terminals of Q1 at 3GHz. The trouble is that everything is
coupled to everything else and I\'m at a loss to tell what
is dominant. Every damn bit of trace around Q1 looks like
a resonator that could be either capacitive or inductive at
3GHz!

At least I\'m convinced that none of the actual /components/
on the schematic are involved in determining this oscillator.
(Except for Q1, of course.) It\'s all in the PCB traces.

Jeroen Belleman

Yes
it is all not so different from the twisted wire oscillator, but mine is simpler:
http://panteltje.com/pub/2.4GHz_twisted_oscillator_IMG_3629.GIF
circuit:
http://www.panteltje.com/pub/twisted_wire_oscillator_IMG_6629.JPG
probably can make my own GHz Doppler RF with that...

When analyzing an oscillator, I always start by identifying
the reactances between BE, EC and CB. (Or whatever the equivalent
nodes are on the actual gain element.)The first pair should
have the opposite sign from the last, i.e., if the BE and EC
reactances are capacitive, the CB reactance should be inductive
and we have a Colpitts. In the reverse case, we have a Hartley.

Any of the reactances could be a resonator of some sort, so
what counts are the reactances at the intended oscillation
frequency. I often see oscillators that use parasitic elements
for one or more of these reactances. That seems to be the case
in your example too. I usually try to avoid dependence on such
elements when designing an oscillator.

The next step is to get the magnitudes of those reactances and
calculate the loop gain. Of course, they aren\'t pure reactances,
but I usually neglect that at first. Nine times out of ten, that
turns out well enough.

Jeroen Belleman

 

[Jan Panteltje]

On a sunny day (Sun, 09 Jan 2022 12:58:49 +0100) it happened Jeroen Belleman
<jeroen@nospam.please> wrote in <sreilq$mnp$1@gioia.aioe.org>:

On 2022-01-09 11:56, Jan Panteltje wrote:
On a sunny day (Sun, 09 Jan 2022 10:25:32 +0100) it happened Jeroen Belleman
jeroen@nospam.please> wrote in <sre9mc$prb$1@gioia.aioe.org>:

On 2022-01-09 00:51, Clifford Heath wrote:
On 8/1/22 9:43 pm, Jeroen Belleman wrote:
On 2022-01-08 10:53, Jan Panteltje wrote:
PS see https://github.com/jdesbonnet/RCWL-0516

Now I just received some about 3 GHz? (still have to measure
it) doppler motion detectors that work through glass etc. from
a local shop, also for about 2 Euro a piece, on ebay those are
even cheaper: https://www.ebay.com/itm/311911747154 Is using
that frequency even legal here? Plenty of stuff play with!



Interesting gadget. I suppose Q1 does double duty as oscillator and
mixer. The schematics are of no help to figure out how it really
works. Anyone care to comment? The secret is all in the PCB layout
around Q1, clearly.

I believe it\'s the same approach that used to be used by the 10GHz
automatic door detectors that used to trigger automotive radar
detectors. Oscillator and mixer in one device, pick out the audio
Doppler signal.

CH

I gathered that much, yes. I was more interested in a discussion
of the PCB traces and how they work together to make an oscillator
and antenna.

I\'m trying to guess the signs of the reactances between the
terminals of Q1 at 3GHz. The trouble is that everything is
coupled to everything else and I\'m at a loss to tell what
is dominant. Every damn bit of trace around Q1 looks like
a resonator that could be either capacitive or inductive at
3GHz!

At least I\'m convinced that none of the actual /components/
on the schematic are involved in determining this oscillator.
(Except for Q1, of course.) It\'s all in the PCB traces.

Jeroen Belleman

Yes
it is all not so different from the twisted wire oscillator, but mine is simpler:
http://panteltje.com/pub/2.4GHz_twisted_oscillator_IMG_3629.GIF
circuit:
http://www.panteltje.com/pub/twisted_wire_oscillator_IMG_6629.JPG
probably can make my own GHz Doppler RF with that...


When analyzing an oscillator, I always start by identifying
the reactances between BE, EC and CB. (Or whatever the equivalent
nodes are on the actual gain element.)The first pair should
have the opposite sign from the last, i.e., if the BE and EC
reactances are capacitive, the CB reactance should be inductive
and we have a Colpitts. In the reverse case, we have a Hartley.

Any of the reactances could be a resonator of some sort, so
what counts are the reactances at the intended oscillation
frequency. I often see oscillators that use parasitic elements
for one or more of these reactances. That seems to be the case
in your example too. I usually try to avoid dependence on such
elements when designing an oscillator.

The next step is to get the magnitudes of those reactances and
calculate the loop gain. Of course, they aren\'t pure reactances,
but I usually neglect that at first. Nine times out of ten, that
turns out well enough.

Jeroen Belleman

Sure, I am but a neural net and just blob these things down without much maaz.
In the twisted wire oscillator case I started with a longer twisted pair
resulting in a much lower frequency and then cut pieces of until I had the 2.4 GHz.
Basically a wavelength related thing, twisted just to hold it together.
On the PCB of that other thing you also see a feedback path.
But I just think in [ parts of ] a wavelength.
S parameters last time I used those was in school for the exams...
One experiment is worth a thousand hours of theory, no spice in use here for this either.
In the \'twisted\' LOL case maybe a low-pass from the collector will also show Doppler difference frequency
if that twisted pair picks up any reflections.
On their PCB it looks like they somehow couple it to some bigger circular area on the other side of the PCB
to get more radiation.